<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<title></title>
	<style type="text/css">
		*{
			margin: 0;
			padding: 0;
		}
		.g-container > div{
			float: left;

		}
		.g-content{
			margin: 0 200px;
			background: #000;
			color: #fff;
		}
		.g-main{
			width: 100%;
		}
		.left{
			margin-left:-100% ;
			width: 200px;
			background: red;
		}
		.right{
			margin-left: -200px;
			width: 200px;
			background: blue;
		}
	</style>
</head>
<body>

<div class='g-container'>

	<div class="g-main">
		<div class="g-content"> 中</div>
	</div>

	<div class="left">左</div>
	
	<div class="right">右</div>
</div>


</body>
</html>